Indian energy giant Adani says it is still committed to its controversial $16.5 billion Carmichael mine, despite engineering and advisory firm AECOM being asked to "stand down" from its work on the mega-mine and rail project in Central Queensland.

Amid increasing speculation about whether the company will be able to secure finance to deliver the project in Central Queensland, Adani Australia said the AECOM decision was part of the normal workflow of delivering the Carmichael mine.

It follows Downer EDI late last year pulling out of a $2 billion contract to build the 388-kilometre rail line from Central Queensland to Abbot Point coal terminal in North Queensland.

Anti-Adani activists have been encouraged by AECOM being asked to stop work on the Carmichael project. Dominic Lorrimer

A spokeswoman for Adani Australia said AECOM's current phase of the engineering and design for the rail project was now complete, but there was an ongoing commercial relationship with the company. It said it still had 600 staff, consultants and contractors working on the project which would be Australia's largest open-cut mine if it ever gets built.

"AECOM remains an important partner for Adani and we appreciate the quality of the work they have completed to date and look forward to continuing to work with them," the spokeswoman said.

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"It is normal for contractor numbers to change through the life of a project as milestones are reached and stages of work are completed. Meanwhile, a new phase of activity on the project has begun, this involves working with other consultants and advisors to prepare for mine infrastructure construction and operation."

The Adani spokeswoman said the company remained "100 per cent committed to the Carmichael project".

A spokesman for AECOM said they were still contracted to Adani but they were asked to stand down by the company and to do no further design work on the project. At the height of their work for Adani, AECOM had 100 people working on the project.

"We don't know what motivated it, whether it was commercial or otherwise. But it's the client's decision," the AECOM spokesman said.

"We completed the work we had to do and we were asked to do no further design work." The spokesman said the company had been paid for the work completed.

Adani also announced it had relinquished part of its office space in Townsville, but there were still 100 people working in its regional headquarters.

Anti-coal groups seized on the AECOM decision saying it was further evidence the Adani mega-mine - which has become part of the national spotlight about the future of fossil fuel in the nation's energy mix - was doomed.

"Adani Group have shown time and time again that they can't take this slow-moving train wreck forward and should scrap it for good," Greenpeace Australia Pacific campaigner Jonathan Moylan said.

"The Australian people don't want it, the banks won't touch it and now even key partners who stand to profit handsomely are giving up on Adani."

The development of alternative supplies of critical minerals, as well as other joint efforts by Australia and the United States to address Chinese influence in the region, will dominate talks in Washington.